1. Field of the Invention
The present invention relates to electronic apparatuses capable of outputting image information and/or audio information transferred from a portable information terminal, and particularly relates to control over a display screen in response to an interrupt occurring in a portable information terminal.
2. Description of the Related Art
In recent years, multi-function portable apparatuses such as smart phones have been widely used. When such a portable apparatus is taken into a vehicle, the portable apparatus is connected to an electronic apparatus mounted in a vehicle (hereinafter, referred to as a vehicle-mounted apparatus) so that a function implemented in the portable apparatus may become available to a vehicle-mounted apparatus. For example, when a portable apparatus and a vehicle-mounted apparatus are connected through connecting means such as a USB cable, image data of an application shown on a display of a portable apparatus and audio data thereof are transferred to the vehicle-mounted apparatus. The transferred audio and image are then output from the vehicle-mounted apparatus (Japanese Unexamined Patent Application Publication No. 2009-281991).
While audio data and/or image data transferred from the portable apparatus is being output by the vehicle-mounted apparatus, the vehicle-mounted apparatus may be required to detect a factor causing an interrupt in the portable apparatus (interrupt factor). For example, while the portable apparatus is executing a navigation function, the vehicle-mounted apparatus may be required to provide notification of an interrupt caused by an event such as guidance at an intersection. The same is true when an incoming telephone call or an electronic mail is received. Japanese Unexamined Patent Application Publication No. 2003-319020 discloses a technique that provides a notification mode preferred by a user when an interrupt such as receiving an incoming telephone call or an electronic mail by a portable apparatus has occurred.
FIGS. 1A and 1B illustrate an interrupt detection method of the related art. FIG. 1A illustrates an interrupt detection method with hardware having a dedicated interrupt signal line. As illustrated in FIG. 1A, a portable apparatus 10 and a vehicle-mounted apparatus 20 are connected through an audio/image signal line 30 for sending and receiving audio and image signals and an interrupt signal line 32 for sending and receiving an interrupt signal. When an interrupt factor occurs, the portable apparatus 10 changes the voltage level of the interrupt signal line 32 to a high or low level, and the vehicle-mounted apparatus 20 detects the start and end of the interrupt.
FIG. 1B illustrates an interrupt detection method with software using a communication protocol for an interrupt. A portable apparatus 10 and a vehicle-mounted apparatus 20 are connected through an audio/image signal line 30 to send and receive a signal according to an audio transfer protocol, an image transfer protocol, or an interrupt protocol through the audio/image signal line 30. When an interrupt factor occurs, the portable apparatus 10 transfers an interrupt signal to the vehicle-mounted apparatus 20 in accordance with an interrupt protocol, and the vehicle-mounted apparatus 20 detects the start and end of the interrupt.
The so-called terminal mode has been proposed in which when a portable apparatus that is a multifunction information terminal such as a smart phone is connected to a vehicle-mounted apparatus, screen data and audio data relating to an application started in the portable apparatus are transferred to the vehicle-mounted apparatus, and the screen data and audio data are output from the vehicle-mounted apparatus.
A portable apparatus that is a multifunction information terminal is capable of starting two or more applications simultaneously, and may, for example, execute a music play application and a navigation application simultaneously. In this case, the portable apparatus handles a screen of one application in front (foreground screen) and a screen of the other application at the back (background screen). In the terminal mode, the portable apparatus is configured to transfer the front screen information thereof to the vehicle-mounted apparatus. If a music play screen is displayed in front and the navigation screen at the back in the portable apparatus, the music play screen is displayed in the vehicle-mounted apparatus. Audio data generated by music play is transferred from the portable apparatus, and music is output through a speaker of the vehicle-mounted apparatus. FIG. 2A illustrates an example in which a music play screen is displayed on a display 22 of the vehicle-mounted apparatus 20.
If an interrupt such as guidance at an intersection (intersection guidance) occurs in a navigation application being executed in the portable apparatus 10, the portable apparatus temporarily stops the output of audio data for music play and starts the output of audio data for the intersection guidance. Thus, also in the vehicle-mounted apparatus, the audio output for music play is switched to the audio output for the intersection guidance. However, the music play screen of the portable apparatus remains in front. Thus, in the vehicle-mounted apparatus, the music play screen is displayed, preventing display of the intersection guidance screen. FIG. 2B illustrates a relationship between a display screen of the display 22 in a vehicle-mounted apparatus and output audio when an interrupt such as intersection guidance as described above occurs.
Further, when the interrupt detection technique illustrated in FIG. 1A is used, hardware resources may be required for both the portable apparatus 10 and the vehicle-mounted apparatus 20, which increases the costs. When the interrupt detection technique illustrated in FIG. 1B is used, the implementation of a particular protocol for detecting the interrupt may be required, which also increases the costs for the software development. Furthermore, there is a common problem to the methods illustrated in FIGS. 1A and 1B that since audio data/image data and interrupt information are transmitted via different signal lines and/or independent communication protocols, it is difficult to completely synchronize the transmission of an interrupt with the transmissions of audio and image. Further, since an interrupt request is given unilaterally from the portable apparatus to the vehicle-mounted apparatus, it is difficult for the vehicle-mounted apparatus to output audio/images as required.